Greenwich Photoheliographic Results Presentation of sunspot group data Orientation: Solar north is at the top

Solar Drawing

not available

Orientation of the drawings: the small orientation figure (~ in the middle of the page) shows the P position angle of the solar north (N in red) measured eastwards from the terrestrial north point (N in black) of the solar disc.
Ógyalla (1872-1891): Terrestrial north is ~ at the top (N in black) and solar north (N) is in red
Kalocsa (1880-1919): The orientation and its marks in the observational drawings were not standardized. The terrestrial EW and/or solar EW are usually indicated with lines crossing the disk and/or marks at the limb (the relative position of
the terrestrial and solar coordinate systems is the same as that of the black and red ones in the small orientation drawing but they may be rotated with a quantifiable angle in the observational drawing).
If the orientation is indicated ambiguously in a drawing, it can be reconstructed by comparing the various data presented in the related web-page.
Mount Wilson (1917-1976): Solar north is at the top